Liquid cooled amplifier



oct. 27, 197.0 l.. K. FINDLEY 3,536,952

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United States Patent C) m 3,536,952 LIQUID CGGLED AMPLIFIER Lauren K.Findley, St. Petersburg, Fla., assiguor to Electronic Communications,Inc. Filed Dec. 5, 1966, Ser. No. 599,097 Iut. Cl. H015 7/46, 7/26 U.S.Cl. 315-39 5 Claims ABSTRACT F THE DISCLOSURE vide the additionaladvantages outlined in the specification.

This invention relates generally to radio frequency or microwaveamplifiers, modulators, oscillators, and the like, and in particular, tohigh power tubes and their adjunct circuitry.

Industry has long recognized temperature problems inherent indissipating the heat from tubes amplifying, producing, or otherwiseacting upon communication signals. This problem which is nonexistent atlow power levels where the electrodes of the tubes can readily dissipatethe heat, becomes of primary significance at large power levels.Numerous solutions have been proposed and many are in conventional use.These include radiating elements thermally contiguous the tube anode inconjunction with cooling fans and/Or a circulating cooling fluid aboutthe anode. Needless to say, unless suitable precautions are taken, thetube electrodes would become overheated causing the tube to eitherbecome inoperative or drastically shorten its life and efficiency.

Briefly, the present invention is predicated upon the concept ofcirculating a dielectric fluid not only about the tube anode but theremainder of its exterior surfaces and the adjunct microwave circuit aswell. As a consequence, the following advantages are obtained:

(1) Because of the intimate contact between the fluid and the tube andcircuit surfaces, temperature stability of tube and circuit is improvedand thermal drift due to tube and circuit heating is essentiallyeliminated; frequency stability is thereby enhanced and the power levelof operation is uprated.

(2) The adjunct circuitry is concentrated or made smaller since thedielectric (constant) of the fluid is greater than that of air renderingthe microwave circuitry reduced in size.

(3) Critical voltage points on the tube and within the circuit cavitiesare now embraced by a high dielectric (strength) fluid rather than air.Consequently, the voltage breakdown problems prevalent at rarifiedatmosphere (for example, in high altitude planes) are obviatednotwithstanding that the circuits are reduced in size.

(4) Amplifier generated heat may be remotely removed, for example, by aheat exchanger, thus reducing local physical noise inherent in theblowers conventionally used with power tubes having radiating fins.

(5) Corrosion problems, caused by sulphur or salt atmospheres, highhumidity, dust, etc. within critical parts of the amplifier circuit areeliminated, and maintenance is drastically reduced.

(6) Since the dielectric constant of the cooling fluid may be responsiveto temperature variations and in turn control the electrical dimensionof the cavities, the circuit frequency characteristic may be maderesponsive to temperature and accordingly, Vernier tuning may beeffected by critical temperature control.

3,536,952 Patented Oct. 27, 1970 Accordingly, it is the object of thisinvention to provide a means for stabilizing the temperature of amicrowave power tube within practical limits and to effect theadvantages described immediately above.

The above mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will best be understood by reference to the foregoing descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings wherein:

FIGS. 1 and 3 illustrate side and top sectional views (the latter alongline 3-3 in FIG. 1) respectively of one form of amplifier structureemploying the present invention; and

FIG. 2 is a block diagram of a system according to the inventionutilizing the amplifier of FIG. 1.

Referring now to FIGS. 1 and 3, there is shown an amplifier structureincluding a beam power tube 3 designed for forced air cooling by virtueof the radiating element 13. Axially disposed with respect to tube 3 isa pair of concentric coaxial line resonators; tube 5 providing the innerconductor for the outer coaxial tube 4, and the outer conductor for theinner coaxial tube 6.

Electrically, the basic amplifier structure is similar to thoseconventionally known in the art and thuswill be described only insufficient detail to allow an understanding of how this type ofstructure may be modified in accordance with the invention.

Suffice to say, the input and output circuits of the amplifier areformed to include an input tuning annular brass member 7 having mountedthereon contact lingers 7a and a glass rod 9, the assembly forming ashorting plunger of the conventional type; and an output tuning plungerincluding the annular brass member 8, lingers 8a and glass rod 10.Output coupling from the amplifier structure is afforded by means ofdisc 26 which, as is well known, displays the attributes of both a loopand a probe depending upon plunger position, etc.

The structure is hermetically sealed by virtue of the lower end cap 1through which the dielectric cooling fluid is fed (via tube A), andupper end cap 12 through which the fluid leaves the structure (via tube4). The lower end cap is afforded a plurality of channels for dispersionof the fluid throughout the structure. For clarity of explanation,arrows have been applied to the drawings to indicate the directionswhich the fluid takes upon entering the structure. Needless to say onlyan exhaustive amount of views and sections would indicate thecommunication between the various vertical and horizontal communicatingchannels, and accordingly, it will be presumed that communication pointsexist where not shown in the particular view to distribute the liquid asindicated.

The upper end cap comprises a flanged member 11 having fingers 11aspaced upon the inner periphery for contacting and mechanicallyretaining the tube radiator 13. Between flanged member 13 and end plate15, gasket 14 is disposed to hermetically seal this end of theamplifier. Screws 17 (only one of which is shown) are spaced about theperiphery to retain end cap 12 in position with respect to outer coaxialelement 4.

Upon entering the lower end cap portion as described, the fluid isforced up and through the coaxial elements passing between the tuningelements and the associated coaxial tubes by virtue of the spacingafforded by the contact fingers. Since it is desirable that fluidturbulence be maintained at a minimum in order to insure good fluidcontact with heated surfaces, it may prove necessary to add additionalapertures (for example, 21 and 22) to reduce eddy currents.

As may be seen from the figure, the fluid flows generally upwardlythrough the coaxial elements and the ports specifically provided forthis purpose, passing about the tube and in particular, in and aboutradiating element 13, and ultimately passing out the fiuid outlet in theend cap 12.

At this juncture, it bears mentioning that care must be exercised torecognize both the RF leakage problem, as well as the fluid leakageproblem. Thus, for example, with respect to the output element 26, meansmust be provided to insure against leakage of the dielectric fluid tothe output circuit. On the other hand, where ports such as 21 and 22 areintroduced in the internal structure, care must be undertaken not onlyin the placement of the ports, but also in their size to reduce the RFleakage between adjacent stages. In general, the circuit configurationand the tube employed will dictate the input, output, and D C. supplyrequirements which will in turn vary the sealing techniques required.While sealing techniques are well known, illustrative sealing gasketplacement has been shown (SG). The gaskets themselves should be metalwhere possible and otherwise thin to reduce RF leakage.

FIG. 2 illustrates the overall system in block form. From this figure,it may be seen that the fiuid passing upward, from the amplifier fluidoutlet, proceeds to pump 40 from which it is circulated through the heatexchanger 50 which is remotely located with respect to the amplifier toreduce local noise and heat, through the temperature sensing device 60and back to the amplifier at inlet A. Heat exchanger 50 may be of theconventional type with the fluid undergoing sufficient circulationthrough a cool ing environment so that the temperature is reduced thedesired amount. Provisions may be included for capturing air or gases ina reservoir, draining the systems and trapping residue or formedimpurities (although clean dielectric fluids are available).

Since, as a general proposition, the heat loss from a fiuid travellingthrough a heat exchanger depends upon the mass flow rate of the fluid,temperature sensitive element 60 may be employed to precisely controlthe speed of the pump 40 via the control circuit 70. It is specificallyenvisioned that the control circuit 70 may fulfill the function ofeither maintaining the temperature at some predetermined constant, byregulating the fluid displacement effected by the pump 40, or it mayperform the more sophisticated function of tuning the frequency, as willbe described.

To elaborate on the last point, it is well known that the dielectricconstant of most uids depends on the temperature. Accordingly, it ispossible to vary the temperature within the practical limits to finetune frequency. The change in frequency itself is inherent in the changein the dielectric constant since the frequency is dependent upon therelative electrical dimensions of the various components and thesedimensions themselves depend upon the dielectric constant of the mediaembracing such components. Needless to say, this discussion would not berelevant where the dielectric constant remained stable and nodimensional changes are effected by changes in temperature. Thediscussion, however, pointedly illustrates a significant control featurewhich the invention introduces.

For example, temperature sensitive 60 could comprise a thermistor,hermetically sealed and inserted in the flow stream; the output of thethermistor controlling a D.C. amplifier in the control circuit which inturn would control a D.C. motor driving the pump. Auxiliary controlsupon the exterior of the control circuit for superimposing a D.C. levelvoltage would allow Vernier tuning of frequency.

Thus, it may be seen that by modifying conventional microwave amplifiersto permit the circulation of a dielectric fluid around the activeelement (tube) and through the adjunct circuit, the advantagesspecifically recited in the beginning of the specification are provided.The precise dielectric fluid employed may vary widely depending upon thedesired result. A fluid with too great a dielectric constant would causethe physical dimensions of the circuit to assume a size so small that itmay become a practical impossibility to build a device. The dielectricconstant which is too low, on the other hand, would produce very littlephysical reduction in size. A further consideration is a dielectricstrength. That is, since the various components will be reduced in size,it is nec'- essary that the voltage breakdown strength of the mediaemployed be increased in direct proportion. A preferred coolant for thisequipment is known as DC 200 (dimethyl siloxane) which has a dielectricconstant E of 2.78 and is manufactured by the Dow Corning Company. Othersuitable coolants are liquids FC 43 and FC 75 (both inertuoro-chemicals) made by Minnesota Manufacturing and Mining Company andOS 45 (also a dimethyl siloxane) made by Monsanto Company.

It is to be noted that the inventive embodiment depicts the tube as theuppermost component with the anode on top. This is the preferredarrangement since the main heat source is the anode and any tendency ofthe liuid to assume a vapor state will occur here and not in the cavitywhere the electrical effect of the vapor could not be tolerated.

While the principles of the invention have been described in connectionwith specific apparatus, it is to be clearly understood that thisdescription is made only by way of example and not as a limitation tothe scope of the invention as set forth in the objects thereof and inthe accompanying claims.

What is claimed is:

1. A microwave device comprising:

an active element;

at least one of an input tuning circuit and an output tuning circuitelectrically and mechanically coupled to said active element;

an external hermetically sealed housing embracing said element andcircuit;

means including communicating ports through said housing and passages insaid circuit for permitting the circulation of a dielectric fiuid aroundsaid active element and through said at least one tuning circuit; and

heat exchanger means coupled to said housing at said communicating portsfor circulating said fluid between said exchanger means and saidhousing.

2. The improvement claimed in claim 1 further comprising means forsensing the fluid temperature; and means responsive to said temperaturesensing means for regulating the temperature of said fluid.

3. The improvement claimed in claim 2 wherein said temperatureregulating means comprises means for controlling the mass lfiow rate ofthe dielectric uid.

4. The improvement claimed in claim 3 further comprising means formanually regulating the fluid temperature whereby the frequency of saidcircuit may be precisely controlled.

5. The improvement claimed in claim 4 wherein said element is a tube andsaid circuit includes at least one resonator.

References Cited UNITED STATES PATENTS 2,475,035 7/ 1949 Linder 333-832,747,091 5/1956 Fraser 315-116 X `2,884,603 4/1959 Bird et al. 333-223,306,975 2/1967 Donnay 313-12 X JAMES D. KALLAM, Primary Examiner R. F.POLISSACK, Assistant Examiner U.S. Cl. X.R.

